S3-2.4 Friday, Jan. 4 High altitude feeding by Brazilian free-tailed bats (Tadarida brasiliensis: Molossidae, Chiroptera) on migratory populations of insects MCCRACKEN, Gary/F*; WESTBROOK, John/K; LEE, Ya-Fu; GILLAM, Erin/H; JENSEN, Michael/L; BALSLEY, Ben/B; Univ. of Tennessee; USDA-ARS; Univ. of Tennessee; Univ. of Tennessee; Univ. of Colorado; Univ. of Colorado email@example.com
Because the ultrasonic frequencies that bats emit are attenuated within a few tens of meters, most field studies monitoring the echolocation calls of insect-eating bats have been restricted to activity occurring close to the ground. We report a total of 50.2 hrs of recordings from radiomicrophone bat detectors suspended from free-floating helium balloons and from kites. The data include a total of 20,399 echolocation calls of bats from ground-level to 1,118 m above ground level (AGL). Linear regression shows no relationship between recording efforts versus altitude, indicating that our recordings are not biased toward lower or higher altitudes. Linear regression also shows no significant association between the numbers of calls recorded/min versus recording altitude. When examined by 100 m altitudinal intervals, significant differences are documented in recording efforts at different altitudinal intervals, and in bat activity at different altitudinal intervals. Bat activity was greatest at ground level and 400-499 m AGL, with a reduction in activity at 100-399 m AGL. Feeding buzzes, indicating feeding on aerial prey, were most abundant near ground level and at 400-499 m, but were detected at altitudes of ca. 1,000 m AGL. Tracking radar, NEXRAD Doppler radar, and analysis of bat diets using conventional techniques and fecal DNA analysis link the high altitude activity of bats to the high altitude flights of insects, many of which are important agricultural pests.